Plants of the genus Allium and in particular, garlic, have evolved to use various sulphur-containing molecules as agents of defence against tissue damage from microbes and feeding damage from herbivores.
The garlic plant's primary means of chemical defence requires conversion of alliin, a sulphur-containing constituent of the plant by an allinase enzyme. The result of this interaction is release of allicin, an unstable and biologically active molecule containing two sulphur molecules. Allicin in turn converts to more reduced forms of sulphur, such as polysulfides with either methyl or allyl functional groups attached to either end of the sulphur chain.
Molecules with shorter sulphur chain lengths such as diallyl disulfide, dimethyl disulfide and dimethyl sulfide are quite stable, with limited water solubility and can be produced in very high purity by synthetic means. A vast body of literature has identified a range of biological effects from these short sulphur chain length molecules, including repellency, insecticidal effects, physiological effects on plants, stimulatory effects on fungal spore germination and possibly a wide range of therapeutic effects in man, including antibiotic and anti cancer properties.
Polysulfide molecules with higher sulphur chain lengths (S=>3, i.e. containing three or more sulphur atoms) are also very active with increasing evidence of a very wide range of biological activity (insecticidal, nematicidal, mollusicidal, repellent, anti cancer, antibiotic and fungicidal). Numerous groups are starting to examine the biochemistry of the higher chain length polysulfides in great detail with particular emphasis on sites of action for diallyl trisulfide and diallyl tetrasulfide. A recent review of the known and potential activity of polysulfides outlines the area: Münchberg, U. et al, “Polysulfides as biologically active ingredients of garlic”, Org. Biomol. Chem., 2007, 5, 1505-1518.
A consensus is emerging that the polysulfides derived from garlic offer a new group of actives for major new therapeutic products against many forms of human cancer. A similar view on the potential of these molecules as crop protection agents is also rapidly emerging.
Whilst it is possible to chemically synthesize polysulfides ab initio, considerable advantages flow from using polysulfides derived from the parent plant material (e.g. in a garlic extract). Firstly, the use of the compounds within the plant-derived matrix confers some stability to the spectrum of polysulfides. Furthermore, the chemical synthesis of these compounds is complex, and involves handling significantly hazardous materials. The plant-derived material imposes a significantly lower burden on any manufacturing environment, and on the environment generally. There is a need, therefore, for technologies to aid the manipulation, control and optimisation of methodologies for processing garlic and other Allium-derived extracts, and indeed any allicin-containing plant extract such as extracts derived from garlic, onions, leeks, chives, shallots or cabbage. It is among the objects of the present invention to attempt a solution to some of these problems.